For Me First of all 1) It should detect All Viruses and Spywares .(most important) It should scan and detect anything that enters to the system via any medium such as Ethernet or Bluetooth etc. 2) A good firewall which should be easy to configure and troubleshoot. 3) It should be a small program so that it uses less resource. 4) A feature through which I can block files and programs to run so that even if a new threat comes and antivirus unable to detect it but I know what files and process it is using , I can manually block the files and programs to get into a running process till the definition arrives. 5) Antivirus should protect itself from virus. There should be some protection for its own files and virus should not corrupt antivirus.